The invention relates to an apparatus for cold bending pretensioned ferrous and non-ferrous metal sections.
A known apparatus for bending metal sections is disclosed in the German patent No. DE-34 04 641A1 from the same inventor. It is characteristic of this apparatus that the initially straight metal section is adjustably tensioned and that then the tensioned metal section is subjected to rotary bending.
The rotary bending is achieved by pressing a feed rail die with adjustable force against the underside of the metal section, whereby the rotating tool attached to at least one end of the metal section exerted a rotational movement, i.e., a winding movement, and that the tensioned metal section wound around the external perimeter.
With this known apparatus, it was possible for the first time to cold form large and small volume, thin and thick walled sections, with the possibility of bending sections of any shape with a high degree of accuracy in one plane. The basis for the known apparatus is the knowledge that the pretensioning constantly applied during forming equals the shear stress generated in the section during bending and assures a nondeforming bend. An additional advantage is achieved by means of the die rail pressed against the underside of the section during forming in that the coarse grain structure obtained by exceeding the elastic limit of the billet during forming is compressed back to fine grain structure. The forming is thus a type of cold forging which contributes to a strengthening of the billet material during forming by bending. If in fact the coarse structure were retained, modifications of the properties of the material would be inevitable, such as, for example, increased tendency toward brittle fractures. Thus the structural conversion contributes to a reduction in the hardening of the material.
With the known apparatus it was, however, not possible to bend such sections on just any spatial axis; it was also not possible to produce three-dimensionally bent sections.
Furthermore, it was not possible with the known apparatus to form extrusion sections with an undercut groove or a hollow section without deformation of the groove or the hollow section after successful bending.